Electronic article surveillance (EAS) systems are generally known in the art for the prevention or deterrence of unauthorized removal of articles from a controlled area. In a typical EAS system, EAS markers (tags or labels) are designed to interact with an electromagnetic field located at the exits of the controlled area, such as a retail store. These EAS markers are attached to the articles to be protected. If an EAS tag is brought into the electromagnetic field or “interrogation zone,” the presence of the tag is detected and appropriate action is taken, such as generating an alarm. For authorized removal of the article, the EAS tag can be deactivated, removed or passed around the electromagnetic field to prevent detection by the EAS system.
EAS systems typically employ either reusable EAS tags or disposable EAS tags or labels to monitor articles to prevent shoplifting and unauthorized removal of articles from the store. The reusable EAS tags are normally removed from the articles before the customer exits the store. The disposable tags or labels are generally attached to the packaging by adhesive or are located inside the packaging. These tags typically remain with the articles and must be deactivated before they are removed from the store by the customer. Deactivation devices may use coils which are energized to generate a magnetic field of sufficient magnitude to render the EAS tag inactive. The deactivated tags are no longer responsive to the incident energy of the EAS system so that an alarm is not triggered.
For situations where an article having an EAS tag is to be checked-in or returned to the controlled area, the EAS tag must be activated or re-attached to once again provide theft deterrence. Because of the desirability of source tagging, in which EAS tags are applied to articles at the point of manufacturing or distribution, it is typically preferable that the EAS tags be deactivatable and activatable rather than be removed from the articles. In addition, passing the article around the interrogation zone presents other problems because the EAS tag remains active and can interact with EAS systems in other controlled areas inadvertently activating those systems.
Radio-frequency identification (RFID) systems are also generally known in the art and may be used for a number of applications, such as managing inventory, electronic access control, security systems, and automatic identification of cars on toll roads. An RFID system typically includes an RFID reader and an RFID device. The RFID reader may transmit a radio-frequency carrier signal to the RFID device. The RFID device may respond to the carrier signal with a data signal encoded with information stored by the RFID device.
While the use of a spiral antenna alone has its benefits, the coupling mechanism depends mainly on the electric E field and not the magnetic H field. In some instances, the overall RFID read performance is optimized for the far field and the resulting near field read performance may be limited. That is, the antenna cannot be optimized for both the far field and near field. The near field performance depends on how the antenna was designed for the far field. For combination EAS/RFID tag applications, a spiral antenna may limit the various options for near field antennas used in detachers and other POS applications where close proximity read performance is especially important.
The open antenna structure of a spiral antenna allows low frequency or static electric E field to develop a substantial voltage across the RFID chip and this can cause failure of the device if the level is high enough. Such ESD (electrostatic discharge) can occur in the processes of label manufacturing or ultrasonic welding of the hard tag housing.
The market need for combining EAS and RFID functions in the retail environment is rapidly emerging. Many retail stores that now have EAS for shoplifting protection rely on bar code information for inventory control. RFID offers faster and more detailed inventory control over the bar code. Retail stores already pay a considerable amount for hard tags that are re-useable. Adding RFID technology to EAS hard tags could easily pay for the added cost due to improved productivity in inventory control as well as loss prevention.
What is therefore needed is an RFID antenna design for use in an EAS/RFID interrogation system that increases near field read performance without sacrificing far field read performance, while at the same time reducing the likelihood of chip failure due to the build up of electrostatic discharge.